Multi-jabs pose no risk to babies, say US researchers

A baby's immune system could safely cope with as many as 10,000 vaccines at any one time and is not at risk from the current practice of giving combinations such as measles, mumps and rubella together, according to a paper in the influential American medical journal Paediatrics.

A baby's immune system could safely cope with as many as 10,000 vaccines at any one time and is not at risk from the current practice of giving combinations such as measles, mumps and rubella together, according to a paper in the influential American medical journal Paediatrics.

Take-up figures for the MMR jab which all babies are offered at 15 months of age have slumped dramatically in the UK because of parents' fears of an alleged but unproven link to bowel disease and autism.

Many parents are anxious that combinations of vaccines may overwhelm their child's immune system and have sought to obtain the vaccines separately, which the Department of Health strongly opposes.

The paper in Paediatrics is a result of similar concern over multiple jabs in the US, where surveys have shown that around a quarter of all parents have doubts.

But the authors, Paul A Offit from the section of infectious diseases at the Childen's Hospital of Philadelphia and colleagues, say that babies' immune systems are capable of responding successfully to a vastly bigger challenge than the series of triple vaccinations - not just MMR but also diptheria, tetanus and whooping cough (given together with the Hib jab for one form of meningitis) they get before they are two, and the boosters that follow just before starting school.

"Current studies do not support the hypothesis that multiple vaccines overwhelm, weaken, or 'use up' the immune system," says the paper. "On the contrary, young infants have an enormous capacity to respond to multiple vaccines, as well as to the many other challenges present in the environment.

"By providing protection against a number of bacterial and viral pathogens, vaccines prevent the 'weakening' of the immune system and consequent secondary bacterial infections occasionally caused by natural infection."

From before birth, babies develop the ability to respond to a large number of antigens - any molecule recognised by the immune system as "foreign". The authors calculate that if each vaccine contains 100 antigens, the immune system of the baby could respond theoretically to as many as 10,000 vaccines at one time.

"Of course, most vaccines contain far fewer than 100 antigens (for example, the hepatitis B, diptheria and tetanus vaccines each contain one antigen), so the estimated number of vaccines to which a child could respond is conservative," they say.

"By using this estimate, we would predict that if 11 vaccines [the norm before two years old in the US] were given to infants at one time, then about 0.1% of the immune system would be 'used up'." In fact, they add, no part of the immune system is ever used up, because the cells that fight infection are constantly renewing themselves.

Children are, in fact, exposed to fewer antigens in vaccines today than they were in the past. The old smallpox vaccine, which is no longer given because of the eradication of the disease worldwide, contained about 200 proteins. The 11 childhood vaccines given in the US contain fewer than 130 proteins in total.

If multiple vaccines overwhelmed the immune system, scientists would expect the vaccines to generate a less effective immune response in the child than they do when given singly. But combinations such as MMR together with diptheria, tetanus and pertussis (whooping cough) give children as much immunity when given together as when given singly, the authors say.